I. Field of the Invention
The present invention relates generally to abradable coatings, and methods for providing improved adhesion of those coatings, abradable dry film lubricant, with the method for applying and articles made therefrom.
II. Description of the Related Art
The efficiencies of pumps, pistons or compressors rely on the relative movement of internal components against one another to pump liquids or compress gases. For the highest operating efficiency of such devices, it is necessary to minimize leakage between the movable components without having contact between the components. In some devices it is also advantageous to provide a lubricant film to minimize friction between the movable components and/or between the components and the fluid being transferred.
Abradable coatings on the working surfaces of the pumps grind themselves into nearly perfect fitting surfaces when the pump is first operated. Conventional abradable coatings are made of liquid materials which are sprayed or painted onto the working surfaces. Alternatively, the working surfaces can be dipped into the liquid abradable coating composition. The liquid coating may even be electrostatically painted on.
However, these prior art liquid compositions have inherent problems, including adhesion issues, cost for excessive material, environmental concerns arising from the use of the solvents, and the inability to recycle and re-use any overspray, which is surely generated during any spraying or electrostatic applications. Dipping and roller painting may not generate much overspray, but they certainly generate a lot of toxic solvent fumes.
Prior methods are not without their problems, including undesirably high manufacturing costs. For instance, when solvent-based formulations are used, removal, containment, and special handling of the solvent is required. Removal of the solvent (or volatile organic compound) from the coatings—which is completed before the curing process—requires additional heat, time, and handling equipment. The volatile organic compound requires additional care in handling for the safety and health of the operators and the environment. In addition, there is typically significant shutdown time necessary for cleaning and maintenance of solvent-processing equipment. Aside from the problems with processing with solvents, solvent-based materials also create unique problems and additional cost when transporting the materials. There is an additional issue with the thickness of the coating is that they are limited because a thicker coating will sag and run.
Although any water-based system may be more environmentally favorable, there remains additional cost and time of evaporating and handling the water from the coatings and the shutdown time for cleaning and maintenance of the equipment. Furthermore, not all resins can be formulated into water-based systems, so the types of resins available to use with water-based systems are limited.
Another disadvantage of spray coating liquid-based formulations is that it is not practical to recycle any overspray. Reclaimed overspray would require an inordinate amount of re-formulation to adjust its viscosity in order to achieve consistent coating results.
Therefore, there is a need for improved abradable coatings, methods of making and adhering the coatings, methods of coating articles with abradable coatings, and the coated articles themselves. It would be advantageous if the improved coatings were easy to apply, cost effective, energy-wise, used relatively inexpensive and simple equipment, and were environmentally favorable. It would also be advantageous if the composition for forming the abradable coatings was recyclable, to reduce loss during the coating process. Still a further advantage would be realized if the lubricity of the coating could be controlled to best meet different applications.